Directive radio system



. April 6, 1937. E B U E 2,076,222

DIRECTIVE RADIO SYSTEM Filed Aug. 16, 1933 Sheets-Sheet 2 FIG. 5

SELECTIVE ass/42,4709- FAD/N6 56 057507005 INDICATORS A G N 56- CON lkOL54 5s L FIELD FIG 3 STRENGTH 35 HEAVISIDE LAYER l H (2a EARTH "2 6 87 asas lNl/EN TOP 5. BRUCE AT TORNEV Patented Apr. 6, 1937 UNITED! STATESPATENT OFFIL'C E 2,07 6,222 DIRECTIVE RADI'OHSY'STEM Edmond Bruce, RedBank,

Telephone Laboratories,

N. J., assignor to Bell Incorporated, New

York, N. Y., a corporation of New York Application August 16,

22 Claims.

l This invention relates to radio communication systems and moreparticularly to methods of and means for eliminating fading effectsingeneral referring to similar fading at all frequencies in a band offrequencies containing the 1 carrier and sidebands, and the termselective to unlike fading within this band. It is now more or lessaccepted that general fading occurs asa result of changes in thetransmission medium or as a result of extremely small variabil- 5 itiesin the length of the various transmission paths which the waves travelin reaching the receiver and. especially those which initially possesssmall length differences, these differences corresponding to radiofrequency wave lengths. Selective fading is occasioned to some extent bya rapidly varying wave polarization and principally, applicant hasdiscovered, by relatively small fluctuations in the length of theparticu-v lar multiple paths which initially possess large differencesin' their respectivelengths.

Inthe past" Various systems. designed for overcoming general and/orselective fading have been employed with some success. In Patent1,778,750 granted to me on; October 21, 1930;

there is disclosed a system designed especially for eliminating generalfading and employing a.

gain control device; and in a copencling application of J. S. Stone,Serial No. 460,172, filed June 10, 1930, a diversity system, designed toeliminate selective fading and utilizing phase shifters and differentlydirected unilateral an-- tenna units, is described. It appearsdesirable, however, to-eliminate fading, especially selective whichcomprise a single antenna having a directivity as great as ispractically obtainable, and in future systems to receive radiant energywithout fading effects utilizing a single, simple and inexpensiveantenna unit .and a minimum ofequipment associatedtherewith.

It is one object of this invention to improve radio communication.

it is another object, of this invention to eliminate general andselectivefading-in a simple, more economical and more satisfactorymanner than heretofore achieved and at all times, substantially duringthe period of reception.

0' eliminatefading at a distance receivingstation utilizing means at thetransmitting station,

It isa further object of this invention. to receive continuously I. ergypermissible witho tv introducing objectionfading, in. receiving systemsnow being; used It is still another object of this invention to themaximum amount. of en.--

1933; Serial No. 685,340

able fading effects, at all times, substantially,.

during. the. receiving period.

According, to one feature of. this, invention a maj or lobe of adirective receiving antenna, such as the rhombic antenna disclosed in mycopending application, Serial No. 513,063, filed February 3, 1931, issteered or directed so as'to select only one of several wave directionsincluded in the same vertical plane. When the spacing between theadjacent incoming wave directions included in a' wave cluster is lessthan the width of the lobe, as is usually the case, the lobe is steeredsothat-an edge portionthereof includes an, outermost,.either the loweston highest, wave direction. and the radial portion containing thelongest radius,.or principal axis, avoids the cluster. Upon a materialchange in the outermost wave direction or in the spacing of the wavedirections in the cluster, the lobe is redirected in accordance with thechange and so as to achieve reception as at first obtained. Steering isaccomplished by changing the value of an antenna dimension upon whichthe directive characteristic is at least partially dependent and; in thecase' of the rhombic antenna, by varying the side apex angle, or theside length,

or the antenna height above ground. A fading indicator is associatedwith the directive antenna. For the purpose of easily determiningWhemobjectionable fading exists and also for insuring continuous maximumenergy absorption by the directive antenna and at the same time minimumfading, a non-directive comparison antenna connected to another fadingindicator is employed.

According to another feature of this invention a major lobe of adirective transmitting antenna is steered with respect to a particularreceiving station so as to insure, at the receiving station, receptionfrom one direction only. The transmitting antenna may also be steered soas to establish at the receiving point a field of maximum intensity whenreception in one direction only is obtainable.

Additional objects and features of the invention will be apparent fromthe following detailed specification taken in connection with theaccompanying drawings on which like reference numerals designateelements of similar function,

and

Fig. 1 illustrates a rhombic antenna and one means for steering itsmajor lobe;

Figs. 2A, 2B, and 2C illustrate the different positions with respect toan incoming wave clus-- ter which may be assumed by the same major lobeof theantenna illustrated in Fig. 1;

Fig. 3 illustrates the method of eliminating fading at a distantreceiving point utilizing means at the transmitting station;

Fig. 4 illustrates a rhombic antenna and a different means for steeringits major lobe;

Fig. 4A is a plan cross-sectional View of one of the roller assembliesand supporting poles employed in the system of Fig. 4;

Fig. 5 illustrates a complete receiving system comprising a directiverhombic antenna and a comparison antenna; and 4 Fig. 5A illustratestypical indications as obtainable on the fading indicators employed inthe system of Fig. 5.

Referring to Fig. 1 reference numeral I designates a rhombic antenna ofthe type disclosed in my copending application mentioned above,horizontally oriented so as to absorb horizontally polarized wavecomponents. Each side 2 of antenna i has a length 1 approximately equalto its projection on the path or direction included in the verticalplane of wave propagation plus a half of the operating wave length A, asdescribed in my Patent 1,899,410 issued on February 28, 1933. Thedirection of extension of each leg or side 2 is such as to provide adistributed phase shift, with respect to a particular output point, forthe elemental energies absorbed by the side. The vertical plane of wavepropagation is defined as the plane passing through the transmitting andreceiving points and the arc of the great circle connecting said points,and will hereafter be designated as the vertical incident plane.

References numerals 3, 4, and 5 designate resistances which constitute afar-end or terminating distributed impedance, the function of theterminating impedance being to render the antenna unilateral. For thepurpose of overcoming undesirable capacity effects and also for promot-.ing greater unidirectivity the terminals of the distributed impedanceare separated as much as practicable by inserting resistance 3 in onefar antenna side, resistance 5 in the adjacent far side and resistance 4between these two sides at the far-end apex. When the power to bedissipated by the terminating impedance is large, as in the case of atransmitting antenna, an iron wire line may be employed in place ofresistances 3, 4, and 5. The rear-end antenna terminals are connected bymeans of transmission line 6 to a translation device I which may beeither a transmitter or receiver. The antenna I is supported at adistance H above ground 8 by means of guy wires 9, I 0, and I I andwooden poles I2, as will be explained in greater detail later. NumeralsI3 designate insulators included between the antenna I and the guy wires9, Ill, and II.

While the rhombic antenna described above is especially suitablefor-practising the invention it should be understood here that theinvention is not to be limited to this type of antenna inasmuch as itwill be apparent to those skilled in the art that other types ofantennas including antennas arranged for absorption of vertically orcircular polarized components may be successfully employed.

The directional characteristic, Ir, for antenna I is given by thefollowing equation:

Where Ir=current at the point connected to the translation device. K=aconstant.

\=the operating wave length. H=height of the antenna above groundanantenna dimension. 6=angle above the horizontal in the vertical incidentplane of the incoming wave. =one-half the side apex angle-an antennadimension. l=the length in wave lengths of one side of the rhombicantenna=an antenna dimension.

In the above equation there are four variables, three of which are theantenna dimensions H, Z and and the other of which is the wave angle 6.The angle as used herein corresponds to the angle 5, as defined inapplicants above mentioned patent only whens equals 0, that is, onlywhen the direction of maximum antenna action is in the plane of theantenna conductors. When the path or direction of the desired waveintercepts the plane of the rhombic antenna and when the maximumdirection of antenna action coincides with the path, the angle betweeneach side conductor and the path of the wave, that is, the criticalangle defined and designated in the above-mentioned patent, diifers invalue from as used herein and may be conveniently designated 1//. Also,for convenience the complement of may be designated s and the complementof 1,11 may be designated 7, being equal to it and s being equal to ywhen 6 equals zero. The lobe elevation angle, that is, the angle betweenthe plane of the antenna conductors and the principal lobe axis ordirection of maximum antenna action may be designated w. w equals 6 whenthe principal lobe axis coincides with the arrival direotion or path ofthe desired or maximum wave. See Figures 2A and 5.

Assuming a constant value for H, a value of l as given above and asingle Wave angle 6, it can be shown mathematically that, regardless ofthe value of H,

maximum obtainable and is the incoming wave direction. Consequently,where antenna I is used for receiving purposes tion having a known waveangle 6 the antenna is preferably constructed so that 5 equals -6, forthe purpose of obtaining maximum absorption. With a single incoming wavedirection the small amount of selective fading, if any, is caused solelyby polarization variations.

It has been found that an exceedingly large number of energized pathsexists in the ether between the transmitter and receiver. A path is heredefined as the course followed by a single wave of the signal energy.This signal energy emanates from the transmitting antenna in the form ofa large number of waves, the number being dependent upon the sharpnessof the directive major lobe of the antenna. These paths have, at thereceiver, various downcoming wave directions which constitute, as termedherein, a wave fan or cluster. It has been found that the clusterspread, the spacing of the wave directions in said cluster and the anglebetween the mean or central direction in the cluster and. the earthremain relatively constant during a reception period. Assuming twoincoming wave directions in the vertical incident plane, which initiallyhave a large diiference, say thirty-five miles, in their respective pathlengths from the distant transmitter, selective fading occurs at anaudible frequency corresponding to the difference, upon a fluctuation inthe length of either of the two incoming waves. The fluctuation must, ofcourse, be suificient to effect a change in the phase relation of thewaves traversing said paths. It is believed, contrary to the theoryadvanced by others, that the mere difference does not cause thetransient or selective fade although it may cause a constantly increasedintensity, that is a peak, or a constantly decreased intensity,sometimes called a depression, at the frequency in question as comparedto the intensities at other closely adjacent frequencies.

In order to overcome the selective fade the major lobe is deliberatelysteered as explained hereinafter so as to avoid all except one,substantially, of the incoming wave paths included in the cluster. Whenthe spacing between the incoming wave direction is closer than the widthof the major lobe, maximum absorption is unattainable inasmuch as theprincipal axis must then be directed away from the cluster. In such acase reception is accomplished, in effect, by aligning a minor orsubordinate axis of the .major lobe with an outermost wave direction,and preferably the longest minor axis consistent with reception in asingle wave direction. The wave direction is in effect included in anedge portion of the lobe, an edge portion being here defined as any lobeportion exclusive of the radial portion containing the principal axis.

From the above equation it will be apparent that by maintaining any twoof the three variables E, Z and constant, the angle in the incidentplane included between the principal lobe axis and the earths surface orthe plane of the antenna conductors, may be controlled by varying thethird variable. Thus, the major lobe may be steered by varying H, 2 or(1). Moreover, undesired minor lobes may be eliminated by slightlyvarying one of the three dimensions. Varying H or Z an amount sufircientto properly direct the lobe does not change the relation between theside length l and its projection on the wave path included in theincident plane from the 0ptimum value stated above.

Referring again to Fig. l the movable guy wires in connected to the sideapex antenna angles are each associated with a pulley l4 and terminatedin a counterweight l5, each pulley ported at the top of a pole I2. Themovable guy wire ll connected to the far-end apex angle passes overpulley l6 which is supported on another pole l2 and terminates in winchH. Anversible motor I8 is employed for driving the winch IT. Acounterbalanced winch I9 is associated with weight 20 by means of rope2| and pulley 22, for the purpose of governing the speed of winch l1 andpermitting the use of a small motor. The motor I8 is preferablycontrolled froma distant point at which point an indicator, notillustrated, is provided for automatically indicating the value of theside apex angle An automatic safety device, also not illustrated, isprovided at the control point for limiting the movement in eitherdirection of the guy wire ll. Numerals 23, 24, and designate wavedirections included in the vertical incident plane and incoming toantenna I when the antenna is employed for receivingpurposes.

Referring to Figs. 2A, 2B, and 2C, reference 7 5" numerals 26 designatethe same major lobe of the l4 being supand 39.

directive antenna 1 and numerals 23, 24, and 25 designate, as in Fig. 1,the downcoming wave directions which constitute an incoming. wavecluster. Numerals 21 designate the principal lobe axes and numerals 21designate minor or subordinate axes.

When the system of Fig. 1 is employed for receiving energy, eliminationof as follows:

The side apex angles of the rhombic antenna l are, if necessary, firstslightly varied by means of motor [8 to eliminate minor lobes. They arethen similarly varied an amount sufficient to cause the sides 2 toassume, for example, the positions indicated by dotted lines 2, andprincipal axis 21 of the major lobe 26 to align with an incoming wavedirection as, for example, direction 24. If the spacing between wavedirections 23, 24, and 25 is wider than the width of the lobe, as shownin Fig. 2A, the principal axis 21 is maintained aligned with the chosenwave direction, the lobe being redirected whenever necessary inaccordance with the directive changes of said wave direction. If thewave direction spacing is less than the lobe width, as shown in Figs. 2Band 20, the side apex angles are further varied so as to cause the majorlobe to include only one outermost wave direction of suitable fieldstrength, for example, direction 23 in Fig. 2B or direction 25 in Fig.2C. Stated differently, the lobe is steered so that only one minor axis21' aligns with an incoming wave direction. In addition the lobe iscaused to intercept the included wave direction at a point as close aspracticable to the principal axis 21 and, at the same time, to avoid theadjacent'wave direction 23, as explained above. In practice it has beenfound that weak waves having extreme outermost positions in the clusterand sometimes included in the edge lobe portion along very short minoraxes do not materially interfere with the reduction of selective fading.Obviously, the lobe may be steered so as to approach the chosenoutermost direction from a point entirely outside, as well as from apoint within, the cluster.

Referring to Fig. 3, reference numeral 28 designates the surface of theearth included between a steerable transmitting rhombic antenna 29, suchas that illustrated in Fig. l, and a distant receiving rhombic antenna30 which is preferably steerable. Antenna 29 is connected by means offading is achieved 7 line 3| to a transmitter 32 and antenna 39 is 7connected by means of line 33 to a receiver 34. Numeral 35 designates areflecting surface such as the Heaviside layer. For convenience onlytworefiecting surfaces, the earth and the Heaviside layer, areillustrated although it is now more or less established that otherreflecting surfaces or layers exist. The transmitted major lobe ofantenna i may be steered, as explained in connection with Fig. 1, so asto cause its principal axis to align with any one of the outgoing wavedirections 36, 3'11, 38 or 39.

Reference characters P36, P31, P38, and P39 designate paths in the etherwhich have, respectively, at the transmitter the outgoing directionsindicated by arrows 36, 31, 38, and 39 and near the receiver thedirections indicated by 36, 31', 38, Directions 36 and 38', it will benoted, are incoming to antenna 31], so that paths P36 and P33 actuallyinclude or connect antennas 29 and 30. On the other hand directions 3'!and 38' avoid antenna 30 so that paths P31 and P39 do not constitutepaths between these antennas. As illustrated, and as is now wellunderstood, several reflections occur in the energized paths P36, P31,

' paths exist in the ether.

P38, and P39. It may be noted here that regardless of the degree ofconcentration obtained in radiating energy into the ether it has beenfound that, invariably, several distinct paths become energized as aresult of the radiation.

Assuming now that the outgoing direction 31 aligns with the principalaxis and outgoing directions 36 and 38 align with an upper minor and alower minor axis of the lobe, respectively, path P39 being unenergized,any small variability in the lengths of the paths Pas or P38 tracedby'the waves will, as explained above, result in selective fading. Toovercome such fading, the major lobe of the transmitting antenna isdirected so that its principal axis coincides with outgoing direction 38and the two said minor axes with directions 31 and 39, path P36 nowbeing unenergized. With this adjustment, only a single incoming. wavedirection 38', which also corresponds to the direction of maximum fieldstrength, is effective at the receiving antenna 38. As alreadyexplained, the reception of a single incoming wave direction at thereceiver insures the elimination of selective fading. The steerablereceiving antenna 30 is preferably adjusted for optimum reception of thesingle incoming wave direction 38'.

The steerable transmitting antenna 29 employed in the system of Fig. 3is also useful for other purposes than the elimination of selectivefading. Often the condition of the transmitting medium is such thatreception during certain periods is accomplished at antenna 30 only whenenergy is transmitted from antenna 29 in a particular direction as, forexample, direction 36. In such a case, the principal axis of the majorlobe is caused to align with the particular or free direction 35 for thepurpose of establishing a field of maximum intensity at antenna 30. Theenergy transmitted along impeded path P38 does not cause selectivefading since it does not reach antenna 30.

Numeral 40 designates, by way of further explanation, a point at whichreception occurs in one direction only, even when several energized Totransmit to point 49, the principal lobe axis should be aligned with apath having an incoming direction 36" at point 40. Numeral 4idesignates, by way of comparison, a receiving point at which,ordinarily, extreme selective fading occurs.

Referring to Fig. 4, an alternative arrangement for steering the majorlobe of a rhombic antenna, utilizing means for varying the antennaheight, is illustrated. The rhombic antenna l is similar to thatillustrated in Fig. 1 and is supported by means of guy wires 32 eachconnected to an arm 3 which in turn are movably mounted on poles E2. Thefour arms 43 are each connected to a pair of rollers M, each pair beingarranged to travel vertically in a track 45 included in pole l2, asshown in Fig. 4A. Reference numeral 46 designates ropes, preferablynon-conductive, which are wound on drum 4?, the supporting structure forwhich is not illustrated. Each of ropes 46 is connected over pulleys 38and 49 to a different arm 38. Pulley wheels 50, the supports for whichalso are not illustrated, are provided for the purpose of insuringproper travel of the ropes 46 associated with the side apex antennaangles. Reference numerals designate counterweights which are connectedby means of ropes 52 to arms it. These counterweights assist in loweringthe antenna I. Ropes Q6 and 5! are securely fastened to arms 43. Thereversible motor 18 actuates drum 41. Safety devices, not illustrated,are preferably provided for limiting in both directions the movement ofdrum 47.

In operation, the motor l8, which is controlled from a distant point, asin the system of Fig. 1, is caused to move the transmitting or receivingantenna I to a position as, for example, that illustrated by dottedlines 2", at which position the direction of the antenna major lobe issuch as to eliminate selective fading. Obviously, the same rhombicantenna may be equipped, if so desired, with both steering means, asillustrated in Figs. 1 and 4, the means being arranged for independentor simultaneous manipulation. Furthermore, means for varying the sidelength Z may be associated with the rhombic antenna, for lobe steeringpurposes.

Referring to Fig. 5 a receiving system especiallyuseful in systemsemploying wobbled wave transmission, such as disclosed in Patent1,454,532 granted to W. E. Beatty on May 8, 1923 is illustrated.Reference numeral i designates a horizontal rhombic antenna, which issimilar in construction to that illustrated in Fig. 1 and the major lobeof which is steered by varying the side apex angle 5. Antenna i isconnected by means of transmission lines 6 and 53 to a receiver 54through gain control device 55 which may be of any conventional type, asfor example, the type disclosed in Patent 1,778,750, mentioned before.The antenna l is also connected by means of transmission lines 6 and 56to a selective fading indicator 5'! through oscillator-detector 58 whichis employed for obtaining a wobbled audio wave. Reference numeral 59designates a horizontal comparison non-directive half-wave lengthantenna which is connected by means of transformer iii? and line 6! to aselective fading indicator 62 through oscillator-detector 53. The fadingindicators are preferably of the cathode ray type. Each indicator isarranged to present a rectangular pattern or picture when selectivefading does not exist, the width of the pattern being proportional tothe received field strength and the height proportional to audiofrequency variation, as illustrated in diagram or indication 64 of Fig.5A. Numeral 65 designates a typical cathode ray pattern obtained whensevere selective fading exists. Reference character 66 designates thepath or direction of the desired wave at the antennas I and 59, andreference character 6 designates the angle between the path 66 and thehorizontal plane.

In operation wobbled waves traveling in the vertical incident plane andhaving a downcoming direction 66 are received from the distant stationby antennas l and 55 and conveyed to the associated oscillator-detector,and to receiver 54. The detected wobbled waves are supplied,respectively, to indicators 5'! and 62. If the indication on indicator62 is rectangular, selective fading is not present and presumably only asingle incoming wave direction is being intercepted by both antennas. Insuch a case, the major lobe of the rhombic antenna is steered so thatits principal axis aligns with the single incoming direction wherebymaximum absorption is achieved. If the indication on indicator 62 is notrectangular selective fading is present and the major lobe of therhombic antenna l is steered so as to accept one wave direction, thatis, so as to produce a rectangular indication on indicator 5'! andstabilized reception by receiver 54. The observer watches bothindicators simultaneously.

in the transmission medium. .purpose of indicating selective fading, acarrier having a characteristic other than a wobbled ing. This is truesince .Theacomparison-system comprising antenna 59 andassociatedindicator 62 is not essential. It :does provide, however, aconstant and convenient indication of the fading .during the time therhombic antennais being adjusted and during which time thezfadlingmayand often does, disappear. It also enables the operator toobtain, continuously, the maximum permissible absorption of wave energywithout introducing selective fading; and to achieve fading eliminationand'optimum operation without assistance from the transmitter station.To illustrate, after the rhombic antenna has been once adjusted thefading may materially decrease or entirely disappear. Theindicator B2reveals this changed condition and the operator moves the lobe nearer tothe mean or central direction in the cluster for the purpose of aligningthe same Wave direction with a longer minor axis; and, in the case ofcomplete fading disappearance, so as to align it with the-principalaxis.

The systemjust described, as well as the system of Figs. 1 and 4functions to eliminate to some extent, general fading as well asselective fadonly one wave direction is accepted; and general fading iscaused in part by small variabilities in the lengths of the multiplepaths which initially possess small differences, comparable to radiofrequency wave lengths, in their respective path lengths. The gaincontrol 55 functions, as explained in Patent 1,778,750 above mentioned,to further eliminate general fading as occasioned primarily by changesObviously,'for the characteristic as, for example, a tone or pulsecharacteristic and indicators other than cathode ray indicators may beemployed.

The invention described herein has been employed with very satisfactoryresults. In one sys tem waves have been transmitted on a wave length of20.78 meters from station GBW located at Rugby, England and received atHolmdel, New Jersey, by a system similar to that illustrated in Fig. 5,and in whichhe angle 4 was varied between 60 and 70 approximately. Fig.5A, in fact, illustrates typical indications which were received,indication .62 being obtained on the indicator associated with therhombic antenna and indication 63 being obtained simultaneously on thefading indicator associated with the comparison antenna. It isinteresting to note that selective fading elimination increased rapidlyas the degree of fading became greater.

While the invention has been described in connection with certainembodiments it should be understood that it is not to be limited tothese embodiments. Obviously, other transmitting or receiving antennas,either vertically or horizontally positioned and arranged to transmit orreceive vertically or horizontally polarized wave components, may beemployed; and means for steering the major lobe other than thosedescribed above may of course be employed. Moreover, selective fadingand other interference as occasioned by the existence of wave clustersinincident planes otherthan the vertical incident plane as, for example,clusters included in ahorizontal incident plane and resulting from thepassage of the waves through a shadow wall, may besuccessfullyeliminated in accordance with this invention.

What is claimed is:

1. A method of radio communicating which along paths of differentlengths, and receiving at one of the stations, and duringsubstantiallythe entire communicating period, energy propagated along a single path.

3. A method of radio communicating which comprises directing energytoward the Heaviside or similar layer in a plane containing a distantreceiving station and maintaining established at the receiving station,and at all times substantially during the communicating period, a singleincoming radio field.

4. A method of improving radio communication between two stations inasystem comprising a directive transmitting antenna, utilizing means foradjusting the position of a major lobe of the directive characteristicof said antenna, which comprises including in said lobe only one path ofpropagation-having a direction incoming to the receiving station,substantially, and, upon a material directive change in said path at thereceiving station, again including in said lobe only one path having adirection incoming to the receiving station.

5. A method of improving radio communication between two stations in asystem comprising a directive receiving antenna, utilizing means foradjusting the position of a major lobe of the directive characteristicof said antenna, whichv comprises positioning said lobe so as to includeonly one energized path of propagation having a direction incoming tosaid antenna and, upon a material directive change in said path at saidantenna, repositioning said lobe so as to again include only oneenergized path having a direction incoming to said antenna.

6. A method of stabilizing radiant energy absorption by a directiveantenna, utilizing means for steering a major lobe of the directivecharacteristic of said antenna in a plane containing an incoming wavecluster, which comprises aligning one lobe axis only with an incomingwave direction substantially.

7 .,A method of stabilizing radiant energy absorption by a directiveantenna, the effective receiving directions of which are dependent uponat least one adjustable antenna dimension, which comprises adjustingsaid dimension to secure reception in only one direction of wavepropagation, substantially, included in an incoming wave cluster and,upon a change in said propagation direction, again adjusting saiddimension to se cure reception as at first obtained.

8. A method of eliminating fading in a system comprising a receiverconnected to a directive antenna, a major lobe of the directivecharacteristic of which is wider than the spacing between adjacent wavedirections in an incoming wave cluster, utilizing means for moving saidmajor lobe, which comprises including only an outermost wave directionin an edge lobe portion while excluding said cluster from the remaininglarger lobe portion.

9. A method, of eliminating selective fading in i a radio receivingsystem comprising a receiver connected to a directive antenna, utilizingmeans for varying at least one dimension of said antenna upon which thedirective characteristic is dependent which comprises varying saiddimension an amount sufiicient to eliminate undesired minor lobes of theantenna directive characteristic, and further varying said dimension toexclude all except one wave direction included in an incoming wavecluster.

10. A method of eliminating fading in a radio receiving systemcomprising a directive antenna connected to a receiver, utilizing meansfor steering a major lobe of the directive characteristic of saidantenna in a plane containing an incoming wave cluster, the width of themajor lobe being greater than the spacing of the Wave directions in saidcluster, which comprises causing the principal lobe axis to avoid saidcluster and moving said lobe so as to include only an outermost wavedirection of said cluster, substantially.

11. A method of reducing selective fading in a system comprising atranslation device connected to a horizontal rhombic antenna, thedirection of a major lobe of the directive characteristic of which isdependent upon certain antenna dimensions including the antenna heightabove ground and the value of the side apex angles, which compriseschanging the value of at least one of the above dimensions an amountsufficient to receive only one suitable wave included in a wave clusterand upon a material change in said wave cluster, again changing one ofthe above dimensions an amount sufiicient to compensate for said change.

12. A method of receiving Wobbled radiant energy without substantialfading, utilizing a directive antenna connected to a receiver andthrough an oscillator-detector to a cathode ray fading indicator, themajor lobe of the directive characteristic of said directive antennabeing wider than the spacing between adjacent wave directions in anincoming wave cluster, means for moving said major lobe and a comparisonantenna connected through a second oscillator-detector to a secondcathode ray fading indicator, which comprises simultaneously observingthe indications of said indicators to determine the fading condition,moving said lobe so as to obtain maximum reception and minimum fading,substantially, as indicated by the first indicator and upon a materialchange in the indication on one of the indicators again moving said lobeso as to obtain maximum reception without fading.

13. In a radio system, a directive rhombic antenna having sides greaterthan a half-wave length, said antenna having the principal axis of itsmajor directive lobe included in a plane perpendicularly related to theplane of the antenna and containing one antenna diagonal, and means forvarying one of the antenna dimensions on which the position of its majorlobe in said firstmentioned plane is dependent.

14. In a radio system, a directive rhombic antenna, each leg of which isapproximately a half wave-length longer than its projection on the pathof propagation, and means for simultane ously and similarly changing itsside apex angles.

15. In a radio system, a directive horizontal rhombic antenna, each sideof which is equal to a half wave-length plus the projection of the sideon the path of Wave propagation, said antenna being positioned so thatits operation is aiTected by the ground, and means for adjusting theantenna height above ground.

16. In a radio receiving system, a uni-directional rhombic antenna eachleg of which is approximately a half wave-length longer than itsprojection on the path of wave propagation, means for adjusting thedirection of a major lobe of its directive characteristic, said meansbeing adjusted so that said lobe includes only one of several wave pathsin an incoming wave cluster.

17. In a radio receiving system, a rhombic antenna, means for adjustingthe position of the major lobe of its directive characteristic, a firstfading indicator, a receiver, a gain control device, said antenna beingconnected to Said first indicator and through said gain control deviceto said receiver, a non-directive antenna positioned relatively close tosaid rhombic antenna, a second fading indicator, said non-directiveantenna being connected to said second indicator, the position of saidlobe being dependent upon the indications received on both indicatorsand such as to receive a maximum amount of energy Without fading.

18. A method of receiving radiant energy without substantial fading,utilizing a translation device connected to a directive antenna andmeans for varying the position of a major lobe of the directivecharacteristic of said antenna, which comprises including in said lobeat all times substantially only a single energized pathof Wavepropagation and absorbing from the Wave corresponding to said path amaximum amount of energy.

19. A method of improving radio communication between two stationsseparated by a medium in which several paths of different lengths areenergized by one of the stations, which comprises receiving at any giveninstant at the other station energy propagated over only one of saidpaths and compensating for intensity variations in said energy uring thecommunication period.

20. In a radio system, a imidirective rhombic antenna comprising fourconductors having their directions of maximum radiant actionsuperimposed in eiTect in a plane perpendicularly related to the planeof the antenna and containing one diagonal of the antenna, and meansassociated with the antenna for changing in said first-mentioned planethe resulting direction of maximum radiant action of the antenna. 1

21. In a radio system, a directive antenna comprising two angularlyrelated conductors, said antenna having its direction of maximum radiantaction included in a plane perpendicularlywelated to the plane of theantenna anddb'iitaining the bisector of the angle formed by saidconductors, and means for changing in said firstmentioned plane thedirection of maximum radiant action.

22. In a radio system, a directive antenna connected to a translationdevice and comprising a pair of angularly related conductors positionedin the same plane, means for changing the angle between said conductors,said angle being adjusted so that the length of each conductor isapproximately a half wave-length greater than the projection of theconductor on the path or direction of the desired wave and so that theangle between said path and said plane is approximately equal toone-half the angle between said con ductors.

EDMOND BRUCE.

